Isaac Wirgin, study leader from New York University's Department of Environmental Medicine, along with Mark E. Hahn, senior scientist at WHOI, and Diana Franks, WHOI biologist, have found that the Atlantic tomcod, a common fish found in the Hudson River, has not only survived mass amounts of pollution in this river for a long period of time, but has also thrived in this particular environment.

It's common to see insects develop resistance to insecticides, or bacteria to antibiotics, but according to Wirgin, this is the first instance where a member of the vertebrate population has developed a resistance to a hostile environment.

The Hudson River has become polluted partially due to two General Electric facilities releasing 1.3 million pounds of polychlorinated biphenyls (PCBs) over a 30-year period. Now, 50 years later, the Atlantic tomcod is alive and better than ever, and researchers have pinned a single genetic receptor as the reason for the vertebrate's resistance.

Researchers found that a receptor gene called AHR2, which mediates toxicity and controls sensitivity to PCBs, is what made the Atlantic tomcods evolutionary change possible in order to become resistant to PCBs. More specifically, the Hudson River tomcod's AHR2 proteins seem to be missing two of the 1,104 amino acids that are traditionally found in this protein, which weakens the bond between the receptor and the PCBs. Researchers believe this weak bond is what prevents the PCBs from affecting the tomcod in this area.

With PCB resistance, the tomcod is capable of living in this area and reproducing in the winter. But when summer comes around, the tomcod becomes a prime food source for the striped bass and other fish. This is a problem because despite the tomcod's PCB resistance, the fish still absorb these contaminants and can pass them on to those that eat them. Through this transfer, humans who fish and eat what they catch from the Hudson River can consume the contaminants as well.

This isn't the only negative aspect of the tomcod's resistance. According to researchers, this genetic change can make these fish more sensitive to other harmful chemicals like polycyclic aromatic hydrocarbons (PAHs) because the tomcod "cannot degrade them properly."

The AHR2 receptor is a normal part of development for the tomcod, but this type of genetic change that has made the tomcod resistant to PCBs in the Hudson River could have long-term harmful effects on the health of this fish.

"Hudson River tomcod have experienced rapid evolutionary change in the 50 to 100 years since the release of these contaminants," said Wirgin. "Any evolutionary change at this pace is not a good thing."

Cleaning up the river wouldn't be a good thing for the fish either, because the fish would need to adapt to the cleaner environment once again, experiencing more fast-paced evolutionary changes. Researchers are currently unsure as to what these consequences are as far as long-term health goes for the fish during the evolutionary changes.

Recently, an EPA-mandated cleanup of the Hudson River PCBs has begun, which may be troublesome for the tomcod who have developed a variant AHR2 gene specifically for the toxic substance.

They are living fine now. Seems they made a genetic trade to stop what was killing them before to a weakness to something that wasn't killing them yet. Not sure what the human bodies resistance to said chemical is but we adapt well and its filtered through another fish if we don't eat the resistant fish directly."Life will find a way."- Jurassic Park.

Unfortunately it doesn't work that way. The effect of being eaten by another fish actually concentrates the pollutant in most cases. That's why mercury concentrations are very low in the ocean but many species of tuna (a high level predator) contain worryingly high levels of it.

What is rarely ever said though is that most of the toxic chemicals like PCBs collect in the liver and gonadal tissues which humans don't normally eat, unless the processors are just grinding the whole fish up and selling it that way. We had samples in the lab that were supposedly contaminated with PCBs but the meat of the fish had non detectable or barely detectable but not quantifiable levels while the livers did have high levels. If you ground the whole fish up and made the sample that way it was considered high, if you core sampled the meat it was low. It all matters how you look at the sample what you will find.